1. Field of the Invention
The present invention relates to an implantable medical device according to the preamble of the independent claim.
2. Description of the Prior Art
It is known in the field of implantable heart stimulators or pulse generators to use a magnet to change the pacemaker to a predetermined test mode, for indication of e.g. battery condition. Other predetermined modes may for instance be threshold tests or diagnostic data storage etc. When such a test is performed a magnetically strong test magnet is held at the skin of the patient in order to activate a detector. An activation of the detector results in a “magnet ON” detection, which in turn results in a change to the predetermined mode. Such a pacemaker is for instance disclosed in U.S. Pat. No. 4,390,020.
U.S. Pat. No. 5,722,998 discloses an implantable medical device including a GMR sensor that inter alia is used to detect the presence of a magnetic field from a permanent magnet. When a magnetic field is detected the sensor causes the operation of the implantable device to revert to a magnet mode (also referred to as safe mode) of operation in which a predetermined, typically asynchronous, ventricular pacing rate is emitted.
However, some medical interventions might interfere with the function of an implantable pulse generator such as a pacemaker. Examples are electrosurgery, diathermal treatment etc. In these cases one possibility is to program the IPG into a safe mode during the entire intervention. The device according to the '998 patent of course allows this, but at the cost of not allowing the device to be provided with a magnet test mode, since the magnet mode is reserved for the safe mode. The device according to the '020 patent does not allow a safe mode, but does allow the magnet test mode. To obtain a safe mode the device according to the '020 patent the device would have to be extensively reprogrammed by a cardiologist both before and after the medical intervention.